The chairman of Papua New Guinea's land scandal inquiry says flawed leases over millions of hectares of traditional land need to be revoked.

Three commissioners took more than a year to investigate how 11 per cent of the country's land mass was leased out and if landowners had given their consent.

Many of the leases are for 99 years.

In his first interview since the inquiry finished, Chief Commissioner John Numapo told Radio Australia's Pacific Beat that 66 of the 75 leases investigated do not have a valid certificate of alienability.

"They have been unlawfully issued, and therefore the only option left now to the government is to have them revoked as per our recommendations and our findings,' Commissioner Numapo said.

The 66 leases include some investigated by Commissioner Alois Jerewai who failed to submit his final report to government.

Hundreds of thousands of landowners and 5.2 million hectares of land are affected by the leases referred to the Commission of Inquiry.

Many have been used by well-connected logging companies to avoid forestry rules which usually forbid clear felling of forests.

Government delay

The PNG Government received the findings and recommendations of Mr Numapo and Commissioner Nicholas Mirou in June last year.

In September, Prime Minister Peter O'Neill told parliament the inquiry had revealed a shocking trend of corruption and mismanagement.

Mr O'Neill said drastic action was needed but since then has not said if he would revoke leases.

They have been unlawfully issued, and therefore the only option left now to the government is to have them revoked.

John Numapo, Commission of Inquiry chairman

He has referred the inquiry's recommendations to an interdepartmental committee.

Mr Numapo says he's concerned about the delay.

'Those recommendations do have to be implemented because it is affecting the people and especially the customary landowners,' he said.

Many landowners live a subsistence lifestyle and rely on their land entirely for food, shelter and income-generating activities.

'When the report was tabled in parliament I understand the Prime Minister made a commitment to ensuring the recommendations of the Commission of Inquiry is implemented so we are all waiting on that to happen' Mr Numapo said.

The sooner they (the government) move on it the better,' he said.

Mr Numapo called on Mr Jerewai to finish his report.

Whatever financial difficulties the commission suffered 'there is no real excuse for Commissioner Jerewai not to deliver his report,' he said.